Death is when signs of life in an organism cease. It refers both to a specific event an, particularly in humans, to a condition the true nature of which it has for millennia been a central concern of the world's religious traditions to penetrate. Numerous factors can cause death: predation, disease, habitat destruction, senescence, conflict, malnutrition, for example, or mere accidents resulting in terminal physical injury. Principal cause of death in people in developed countries is disease precipitated by aging. The chief concern of medicine has been to postpone and avert death. Precise medical definition of death, however, becomes more problematical, paradoxically, as scientific knowledge and technology advance.